The electrolytical amalgamation of metals directly from aqueous solutions of the respective metal ions is not always feasible, because of hydrolysis and/or precipitation caused by the change of acidity in the course of electrolysis. Therefore, its applicability for metals other than alkali metals, iron and nickel etc. is quite limited.
The electrolytical reduction of metallic ions in aqueous solutions into metallic state taking use of a mercury pool as cathode and an inert metal such as platinum as anode has been well known. The amalgams of alkali metals and transition metals (such as iron, cobalt and nickel etc.) can thus be easily made. However, for many other metals hydrolysis and/or precipitation during the process of electrolysis severely restrict its wider applicability.
Taking uranium as an example, the reduction of uranium ion into metallic state is known to proceed according to EQU UO.sub.2.sup.2.sup.+ + 4H.sup.+ + 6e.sup.- .revreaction. U + 2H.sub.2 O
direct electrolysis using a mercury pool as cathode will unavoidably lead to the elevation of pH or the lowering of acidity and consequently to the precipitation of UO.sub.2 and hydroxides. The chemical reaction is thus prevented from proceeding beyond tetravalent state, U(1V). The conventionally adopted process of extracting uranium ion in aqueous solution by sodium amalgam is rather tedious and gives rather low yield. The uranium ion is exchanged with sodium atoms in the amalgam and thus reduced into metallic state. The highest attainable yield published of late employing this process by Malan et al. gives 50 mgU/mlHg. (J. Inorg. Nucl. Chem. 33 3097 (1974). Here, the elevation of pH is also the main problem to be overcome, since it has been found that the optimum pH range for the uranium amalgamation is narrowly restricted to 3-4. Even though the pH of the electrolytic solution is preadjusted, it will change in the course of electrolysis. In order to keep virtually constant acidity, a specially designed electrolytical cell was constructed and used, which is comprised of two main compartments divided by an ion exchange membrane: anode compartment and cathode compartment. The amalgamation takes place in the mercury-cathode compartment where hydrogen ions are consumed, however, these will be continuously supplied through the ion exchange membrane from the anode compartment. The pH of the electrolytic solution will thus be kept constant.
The thereby obtained amalgam is then thermally decomposed under reduced pressure and/or in an inert gas atmosphere and heated up to the melting point temperature the metal can thus be obtained. The overall process for the production of metal will be greatly simplified as compared with the conventional metallurgy, it has more economical advantages especially for the preparation of rare and precious metals, such as uranium, neptunium and transuranium.